Electric motor

ABSTRACT

An electric motor includes an upper housing, a lower housing including a flange for mounting the upper housing thereon and a cone-shaped portion extending away from the flange and the upper housing. The electric motor further includes a stator assembly formed of a first core having a first height and fitted into the upper housing, a rotor assembly rigidly joined to a shaft to rotate therewith within the stator assembly and formed of a second core having a second height, and a hub connected to a lower end of the shaft to rotate therewith in relation to the cone-shaped portion. The hub is configured to secure an operable implement to the electric motor. The second height is greater than the first height.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.13/554,815 filed on Jul. 20, 2012, which is a divisional of U.S. patentapplication Ser. No. 12/684,617 filed on Jan. 8, 2010, now U.S. Pat. No.8,227,948, which claims priority to U.S. Provisional Patent ApplicationSer. No. 61/143,612 filed on Jan. 9, 2009, all of which are herebyincorporated herein in their entirety.

TECHNICAL FIELD

This disclosure is generally related to electric motor construction, andmore particularly, to electric motors employed in utility vehicles andwalk-behind power equipment, such as lawn and garden tractors, mowers,and the like. The disclosed motors may be used in connection withprimary electric drive systems or auxiliary drive systems that driveauxiliary power devices and various work implements of the vehicle orequipment.

BACKGROUND OF THE INVENTION

Utility vehicles, such as lawn and garden tractors and mowers, havegenerally relied upon internal combustion engines as the prime movertransferring power through mechanical linkages (gearing or belts),hydrostatic drive(s) or other similar devices to propel or drive thevehicle. A deck of the utility vehicle is typically used to employ anauxiliary system, such as cutting blades of a lawn tractor. The majorityof commercial and consumer mowers employ a deck (auxiliary) drive systemusing belts and pulleys driven by an engine typically with an electricclutch/brake to stop or drive the deck system. Other variants take theform of a power take off (PTO) shaft in combination with pulleys andbelts to drive multiple blade spindles in larger decks or toindividually drive spindles with hydraulic motors in multiple deck orreel versions.

Utility vehicles and other equipment incorporating electric motor(s) asprimary mover(s) have emerged as viable alternatives to internalcombustion utility vehicles and equipment, particularly due to risingoil and fuel prices. Consumers also want products with increased comfortand increasing versatility in smaller packages. Electric vehicles offerconsiderable advantages for reduction of emission of noise andpollution, as well as improved operator controls. These vehicles, whichtypically include one or more work accessories or auxiliary systemsincorporating additional electric motors, also incorporate various formsand levels of control, depending upon the vehicle type, drive type,functional features, and other design aspects to ensure safe operation.With the advancement of these vehicle types and their functionality,various problems and needs have arisen in their design, operation, andfunctionality.

Due to their relative high power capacity, three-phase AC electricmotors are typically used in utility vehicles to drive axle shafts orwork implements and are powered by a power source, such as an on-boardbattery pack or array. AC induction motors, and Permanent MagnetSynchronous (PMS) Motors in particular, would be advantageous in utilityvehicle applications due to their power capacities and efficiencies intheir physical constructions. PMS motors have the ability to rapidlyaccelerate and decelerate high-inertial loads, which minimizesprocessing time. Both AC induction motors and PMS motors utilize astator assembly with specially distributed phase windings connected ineither a “wye” or “delta” fashion. Stator laminations minimize airgapreluctance, facilitating a high level of flux coupling between the rotorand stator. The magnetic circuit of the PMS motor is similar to an ACinduction motor. The fundamental difference between PMS and AC inductionis how magnetic poles are produced on the rotor. An AC induction motorinduces magnetic poles that travel along the rotor's surface, a processthat requires a small airgap and consumes a component of applied motorpower. Conversely, PMS motors create stationary poles on the rotor usingfixed high-energy magnets. Permanent magnet rotor construction supportslarger airgaps, reduces the rotor's inertia, and increases motorefficiency by eliminating power consumption associated with ACinduction. Due to these advantages, PMS motors offer significantpotential advantages in utility vehicle applications.

Regardless of the motor type, however, implementation to power auxiliaryfunctions of utility vehicles presents a variety of problems. Thesevehicles often operate in harsh environments that could damage the motorif it is not adequately protected. Furthermore, there is a problem inbalancing the need for powerful electric motors with accommodating thesepowerful motors in a vehicular application, which typically places apremium on reducing size and weight of components. The physicaldimensions and overall size of standard off-the-shelf motors that havethe required power capacities many times present clearance problems forthe vehicle designer or obstructions to the vehicle operator. Presentlyavailable off-the-shelf motor designs that provide sufficient torque areoften too large and/or too heavy to be practical for application to autility vehicle. Additionally, they may not be configured in a suitablemanner to drive the required auxiliary implement(s). With theadvancement of electric-drive utility vehicles and their functionality,the aforementioned problems, as well as other problems and needs havearisen. This disclosure is directed to addressing these and otherproblems in the general area of improved electric motor design and driveconfigurations for utility vehicle applications.

SUMMARY OF THE INVENTION

The present invention comprises an electric motor for use in a utilityvehicle or other power equipment, and in a particular embodiment, anelectric motor for use in performing auxiliary work functions of autility vehicle. These motors are referred to herein as “auxiliarymotors” or “deck motors,” and it will be understood that these terms maybe used interchangeably. In a particular embodiment, an electric motordesign configuration suitable for driving one or more mowing blades isdisclosed. The electric motor is shown in use with an electric lawnmower. While shown and described in reference to utility vehicles, itwill be apparent to those skilled in the art that the electric motordefined herein could be utilized in a variety of other configurations orapplications that require translation of electricity to mechanicalenergy from a compact and efficient motor as shown.

While not limited to a specific type of motor, the deck motors shown inthe illustrated vehicle configurations and component drawings are ACpermanent magnet synchronous (PMS) motors. Aspects of the presentinvention may be applied to other motor types as well, includingbrushless direct current (BLDC), AC synchronous, AC induction,integrated permanent magnet (IPM), switched reluctance, stepper, orslotless brushless type permanent magnet motors.

Features of the disclosed electric motor include a 12-slot statorconstruction with a 10-pole rotor having convex magnets. The statorcomprises a lamination stack that is skewed around the stator axisresulting in a smoother flux-density curve and improved efficiency.Motor winding path, quantity of wraps and wire connections arespecified. Each motor comprises an attached terminal box designed toprovide a low motor height profile, and an integrally formed nose coneon the motor lower housing adapted for connection with the variousdriven implements. A single cupped and finned upper housing is providedfor improved capability and reliability in rigorous turf applications.

The present invention provides an electric motor, which includes anupper housing, a lower housing including a flange for mounting the upperhousing thereon and a cone-shaped portion extending away from the flangeand the upper housing. The electric motor further includes a statorassembly formed of a first core having a first height and fitted intothe upper housing, a rotor assembly rigidly joined to a shaft to rotatetherewith within the stator assembly and formed of a second core havinga second height, and a hub connected to a lower end of the shaft torotate therewith in relation to the cone-shaped portion. The hub isconfigured to secure an operable implement to the electric motor. Thesecond height is greater than the first height.

According to one aspect of the invention, an electric motor stator isprovided which has a stator core having a plurality of teeth and aplurality of slots, each one of the slots formed betweencircumferentially adjacent teeth, and a plurality of winding pairs eachassociated with one of a plurality of power phases, each winding of theplurality of winding pairs wrapping a pair of adjacent teeth. For eachwinding pair, one of the windings wraps a first pair of adjacent teethby (a) entering one of the slots situated adjacently to andcircumferentially outside the first pair of adjacent teeth, (b)alternately wrapping each tooth of the first pair of adjacent teeth and(c) exiting through one of the slots situated between the first pair ofadjacent teeth. The other one of the windings wraps a second pair ofadjacent teeth by (d) entering one the slots situated between the secondpair of adjacent teeth, (e) alternately wrapping each tooth of thesecond pair of adjacent teeth, and (f) exiting through one of the slotssituated adjacently to and circumferentially outside the second pair ofadjacent teeth.

According to another aspect of the invention, a method is provided forwiring a stator of an electric motor. The stator includes a stator corehaving a plurality of teeth and a plurality of slots, each one of theslots formed between circumferentially adjacent teeth, and a pluralitywinding pairs each associated with one of a plurality of power phases,each winding of the plurality of winding pairs wrapping a pair ofadjacent teeth. The method includes wrapping a first pair of adjacentteeth by one of the windings of each winding pair by (a) entering one ofthe slots situated adjacently to and circumferentially outside the firstpair of adjacent teeth, (b) alternately wrapping each tooth of the firstpair of adjacent teeth, and (c) exiting through one of the slotssituated between the first pair of adjacent teeth. The method furtherincludes wrapping a second pair of adjacent teeth by the other one ofthe windings of each winding pair by (d) entering one the slots situatedbetween the second pair of adjacent teeth, (e) alternately wrapping eachtooth of the second pair of adjacent teeth, and (f) exiting through oneof the slots situated adjacently to and circumferentially outside thesecond pair of adjacent teeth.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forth anillustrative embodiment and is indicative of the various ways in whichthe principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a first configuration of a utility vehicleincorporating an embodiment of the present invention.

FIG. 2 is a perspective view of an embodiment of the present invention.

FIG. 3 is an elevation view comprising the embodiment shown in FIG. 2.

FIG. 4 is an exploded perspective view of the embodiment shown in FIG.2.

FIG. 5 is a cross-sectional view along the line 8-8 of FIG. 3, showingpreviously disclosed components assembled.

FIG. 6 is a perspective view of the stator core as shown in FIG. 4,combined with diagrammatic and 2-dimensional views showing the terminalleads, thermistor, and certain wiring details, in order to illustratethe stator assembly.

FIG. 7 is a winding diagram for the basic stator assembly shown in FIG.9.

FIG. 8 is a connection diagram for the basic stator assembly shown inFIG. 9.

FIG. 9 is a perspective view of the rotor and basic stator assemblies.

FIG. 10 is a top plan view of the rotor assembly shown in FIG. 9.

FIG. 11 is a top plan view of the stator core of the stator assemblyshown in FIG. 9.

FIG. 12 is a representative diagram of certain electro-magnetic fluxcharacteristics of the present invention compared to those of adifferent configuration.

FIG. 13 is an exploded perspective view showing the motor shaft anddriven implement adapter.

DETAILED DESCRIPTION OF THE DRAWINGS

The description that follows describes, illustrates and exemplifies oneor more embodiments of the present invention in accordance with itsprinciples. This description is not provided to limit the invention tothe embodiments described herein, but rather to explain and teach theprinciples of the invention in order to enable one of ordinary skill inthe art to understand these principles and, with that understanding, beable to apply them to practice not only the embodiments describedherein, but also other embodiments that may come to mind in accordancewith these principles. The scope of the present invention is intended tocover all such embodiments that may fall within the scope of theappended claims, either literally or under the doctrine of equivalents.

It should be noted that in the description and drawings, like orsubstantially similar elements may be labeled with the same referencenumerals. However, sometimes these elements may be labeled withdiffering numbers, such as, for example, in cases where such labelingfacilitates a more clear description. Additionally, the drawings setforth herein are not necessarily drawn to scale, and in some instancesproportions may have been exaggerated to more clearly depict certainfeatures. Such labeling and drawing practices do not necessarilyimplicate an underlying substantive purpose. As stated above, thepresent specification is intended to be taken as a whole and interpretedin accordance with the principles of the present invention as taughtherein and understood by one of ordinary skill in the art.

FIG. 1 shows an exemplary utility vehicle in the form of a mowingvehicle 50 incorporating a plurality of electric motors. Vehicle 50 hasa single transaxle 40 for driving both rear wheels. Transaxle 40 ispreferably an electric transaxle incorporating one or more electricdrive motors. Vehicle 50 includes a traction controller 29, an auxiliarymotor controller 30, an electric power supply 38, an auxiliary mowingdeck 35, and two deck motors 34. The electrical power supply 38 isgenerically represented as a 48-volt power supply. However, othervoltage configurations are contemplated as well. Operator controls onvehicle 50 comprise a traditional mechanical steering wheel 51, a rockerstyle accelerator pedal 52, and a brake pedal 54, as well as anauxiliary control (PTO) switch 43 to initiate or terminate power to deckmotors 34. Though shown in specific locations on the representativevehicle of FIG. 1, the traction controller 29, auxiliary motorcontroller 30 and the electric power supply 38 may be affixed to othersuitable locations on the subject vehicle. These components areconnected by electrical wiring and/or wiring harnesses, many suitablevariations of which are readily available, well-known, and therefore notshown in the interest of maintaining illustrative clarity. The fractionand auxiliary motor controllers receive and process input signals andgenerate output signals for the single transaxle 40 and deck motors 34,respectively.

In vehicle 50, each deck motor 34 is attached to mowing deck 35 andrespectively drive separate blades 15 suspended under mowing deck 35. Itshould be understood that any number of deck motors 34 may be employeddepending on equipment requirements. Furthermore, it should also beunderstood that each deck motor 34 may drive one or more blades eitherdirectly via an output shaft or indirectly via an alternate transmittingmeans. These components and their connections will be described infurther detail below. Though not a requirement, the terminal connectionportions of each deck motor 34 (illustrated as a flat outcropping shownin phantom line in FIG. 1) is shown oriented approximately towards thecenter of the vehicle so as to better protect the terminal connectionsand any associated wiring from damage and reduce the opportunity fordirect spray during washing of the utility vehicle.

It should be noted that the deck motors 34 may vary in size and/oroutput power depending on vehicle configuration and load requirements.For example, vehicle mowing speed, deck airflow characteristics, numberof blades driven by a single motor, blade design, blade size and othersuch characteristics, all have an impact on deck motor loadrequirements. Additionally, although blade design is not specificallyaddressed herein, it is well known that blades and cutters areconfigured in numerous ways and, for the purpose of this disclosure,include various types of other known cutting devices, such as, forexample, wire, cable, or string arrangements. Furthermore, otherauxiliary equipment or desired applications also will alter motor loadrequirements. Therefore, it will be understood that the presentinvention is scalable and various embodiments incorporate motors ofdiffering sizes amenable to package on a utility vehicle to meet theseload requirements.

It should also be understood that any number of electric motors may beimplemented in the utility vehicle 50 in connection with the primarydrive system or to drive additional auxiliary work functions (blades,blowers, brooms, trimmer, auger, etc.) either directly or using beltingand/or gearing arrangements. Accordingly, it will be understood that oneor more of the motors described herein may be employed across numerousvehicle configurations to directly or indirectly drive a wide variety ofmechanical implements.

As an exemplary embodiment in accordance with one or more principles ofthe present invention, the motor 34 will now be described in moredetail, with reference to FIGS. 2, 3 and 4. The motor 34 in FIG. 2includes an upper housing 56 and a lower housing 57. A terminal boxassembly 80 is fixed to one side of the upper housing 56. The cup-shapedupper housing 56 includes a plurality of threaded cavities around itsperimeter for attaching the lower housing 57 using a plurality offasteners 58. In other embodiments, other known suitable methods offastening upper housing 56 and lower housing 57 together are used. Thelower housing 57 includes a mounting flange 47 and a bell nose cone 45extending away from flange 47 and upper housing 56. Mounting flange 47includes a plurality of holes 19 a (shown best on FIG. 4) through whichfasteners 58 extend to secure the upper and lower housings 56 and 57together. Mounting flange 47 also includes a plurality of holes 19 baround its perimeter for attaching motor 34 to mowing deck 35. In analternative embodiment, flange 47 also includes countersink orcounterbore features (not shown) to receive the heads of the housingfasteners 58 so flange 47 is flush-mounted to the upper surface of amowing deck.

Together, the upper and lower housings 56 and 57 form a two-piece,sealed housing designed to facilitate service and assembly, as well asprovide protection for the internal components of motor 34. Priorelectric motor housing designs often utilized a three-piece housingconstruction consisting of a tube-shaped middle portion with a capsecured to each end. This configuration is generally known as “canconstruction” in the motor industry. The two-piece housing constructionof the present invention provides for improved sealing and thermalconduction over such designs. The approximately central location of theplane of the mounting surface of flange 47 between the two ends of theaxis of motor shaft 20 is particularly useful in achieving a low profileabove the mounting surface, such as a mowing deck. The contact area ofthe circular mounting flange also helps to improve heat dissipation,utilizing the mounting surface as a heat sink. To further improve motorcooling, radial fins are included on the sides of upper housing 56. Inthe embodiment shown, both upper and lower housings 56 and 57 are castaluminum. However, other materials such as steel or plastic, and otherforming techniques, such as stamping or molding, are used in otherembodiments.

As shown in FIG. 2, the terminal box assembly 80 includes a wiringreceptacle 85 and three terminal posts 82—one for each of the threepower phases used to drive the motor 34 via the motor controller 30. Thewiring receptacle 85 provides a plug-type connection for wiring used toconvey thermal information from motor 34. In another embodiment (notshown), additional or other sensed information, such as motor speed orrotor position, is conveyed through a similar plug-type connection. Inthe embodiment shown, the terminal box assembly 80 is mounted on theside of upper housing 56 to achieve a low profile and efficient wiringrouting between motor 34 and controller 30, for example. However, inalternative embodiments, the terminal box may be located on othersurfaces of the motor 34. At its distal end, motor shaft 20 connectswith a hub or adapter 13 (see FIGS. 3, 5 and 13) used to secure anoperable implement to the motor so as to harness the mechanical energyit produces. This connection will be further explained below.

FIG. 4 provides an exploded view showing the internal components ofmotor 34. In addition to the components described above, FIG. 4illustrates additional components such as upper bearing 77, lowerbearing 78, motor shaft 20, rotor assembly 70, stator assembly 60 andwave washer or spacer 59. These components are shown assembled in FIG.5. Upper and lower bearings 77 and 78 are press-fit onto motor shaft 20.As shown, motor shaft 20 includes an upper land or shoulder 23 and alower land or shoulder 24 to facilitate positioning of upper and lowerbearings 77 and 78, respectively. The upper bearing 77 is slip-fit intoa cylindrical pocket 48 formed within upper housing 56 and the lowerbearing 78 is slip-fit into a cylindrical pocket 49 formed within lowerhousing 57. Thus, the upper and lower bearings 77 and 78 work togetherto position and support motor shaft 20 within the assembled deck motorhousing, while allowing it free rotation about the motor shaft axis.

Upper bearing 77 is separated from contact with the inside upper surfaceof pocket 48 by a wave washer 59 so as to reduce axial endplay.Referring to FIG. 5, it will be seen that the rotor assembly 70lamination stack height is greater than the stator assembly 60lamination stack height (and the rotor magnets 73 a and 73 b extendabove and below the stator assembly 60 lamination stack) in theillustrated embodiment to compensate for axial movement of rotorassembly 70 if wave washer 59 flexes. Upper bearing 77 and lower bearing78 are of a well-known variety having an inner and outer ring or raceseparated by a plurality of ball bearings such that the inner race ofeach bearing can rotate relative to the outer race. In some embodiments,bearing 77 and/or 78 are of the sealed variety in order to help prolongbearing life by reducing contamination.

The motor shaft 20 also provides a middle land or shoulder 25 which isused to locate the rotor assembly 70. Thus, the rotor assembly 70 issupported by and fixed to the motor shaft 20, and rotates therewith. Therotor assembly 70 fits inside the stator assembly 60 with an appropriateair gap (labeled AG in FIG. 5) between the rotor and stator to allow forfree rotation of rotor assembly 70 relative to stator assembly 60.Stator assembly 60 is press-fit into upper housing 56 against a land orshoulder 53 formed in the upper housing inner wall. This shoulder 53properly positions stator assembly 60 within motor 34. Upper housing 56is heated for expansion and stator assembly 60 cooled for contractionprior to fitting stator assembly 60 into position. When housing 56cools, it then contracts, tightly gripping stator assembly 60. While thedemonstrated embodiment provides these various formed lands or shouldersto aid in locating components and suggests press-fit and slip-fitconnections, it will be understood that other embodiments may utilizeother means, such as tab and slot joints or adhesives, to form a rigidjoint or connection between motor shaft 20 and rotor assembly 70;between motor shaft 20 and bearings 77 and 78; between upper housing 56and stator assembly 60; between upper housing 56 and upper bearing 77;and between lower housing 57 and lower bearing 78. A combination ofjoining means may also be employed in some embodiments, as needed, inorder to ensure a secure joint between the respective aforementionedcomponents. Furthermore, while motor shaft 20 must be of sufficientlyrigid material to withstand the torsional load requirements of motor 34,it may be formed by various means of any suitable material, such as highstrength steel.

Positioning the lower bearing 78 within pocket 49 of the lower housing57 near the driven load helps place the radial load imposed by themowing deck blades near the lower bearing 78, thereby improving staticand dynamic loading on the bearing, which enhances the life of thebearing. Positioning the bearing in this manner also eliminates thepossible need for a separate bearing external to the motor housing. Asshown in FIGS. 4 and 5, the lower housing 57 includes a rim 46 and aplurality of ribs 44 that are formed in the housing. These features addstrength and stability to motor 34. Rim 46 also enhances the sealbetween upper housing 56 and lower housing 57 by properly locating andcontaining housing seal 79 and providing an overlapping joint with upperhousing 56. Seal 79 is an O-ring, but other types of seals arecontemplated as well. It will be understood that the size, number ofand/or positioning of the ribs 44, holes 19 a, fasteners 58, andmounting holes 19 b vary between embodiments and do not limit the designdisclosed herein. Additionally, it is contemplated that in someembodiments, mounting holes 19 b may be threaded to receive screws orbolts. Some embodiments may utilize locknuts or lock washers and nuts tosecure screws or bolts. Other embodiments may utilize carriage bolts toprevent bolts from turning while tightening nuts. Still otherembodiments may utilize other fastening methods, such as riveting, forexample.

FIG. 4 also illustrates additional components of terminal box assembly80, which include a terminal box 81, a seal or gasket 76, and threeterminal posts 82, each having an integral nut 83, a flexible sealingwasher 75, a rigid washer 74, an eyelet terminal 87 and a separate nut88. Each integral nut 83 is seated in a mating recess 84 that is moldedinto terminal box 81. These mating recesses 84 help prevent rotation ofthe terminal posts 82 during tightening of the nuts 88 in assembly orservice. Optionally, in lieu of nuts 83 and mating recesses 84, terminalposts or studs may be insert-molded as an integral part of terminal box81. Inside the terminal box 81, each terminal post 82 first receives aflexible sealing washer 75 to assist in sealing the terminal box 81, abackup rigid washer 74 which prevents damage to and facilitates thesealing function of the flexible sealing washers 75, an eyelet terminal87 which connects via wiring (not shown) to windings on stator assembly60, which will be described in more detail below, and a separate nut 88to secure the inside connection. The three electric power conductingwires (not shown) from a controller terminate with eyelet terminals (notshown, but similar to terminals 87) which each slip over one of theterminal posts 82 extending from the terminal box 81. In the illustratedembodiment, the posts 82 are physically labeled or otherwise marked A, Band C (or other typical convention) on both the inside and outside ofthe terminal box 81 to help ensure proper three-phase wire leadconnections are made. The eyelet terminals on the power conducting wiresfrom the controller are secured to the exterior of the terminal box 81using nuts (not shown) and lock washers (not shown).

Finally, FIG. 4 illustrates the two-pin wiring receptacle 85 thatfastens to the terminal box 81. Wiring receptacle 85 provides a plugconnection on the outer surface of terminal box assembly 80 forconnection to a controller (not shown). As shown, upper housing 56provides an opening 89 through which wiring from stator 60 is routed forconnection to wiring receptacle 85 and terminal posts 82. Additionally,the thermistor leads 68 extend through the opening 89 and terminate inpin terminals 86 that affix to the inside of wiring receptacle 85. Leads68 provide temperature feedback to the motor controller 30. The otherend of these leads is attached to a thermistor probe 69, which ispositioned relative to the stator assembly 60 to provide the temperaturereadings. In another embodiment, a bi-metallic switch is used instead ofthermistor probe 69. With the proper connections in place and the wiringreceptacle 85 fastened to the terminal box 81, the terminal box 81 issecured against upper housing 56 and sealed by gasket 76 or anotherknown sealing method. Terminal box 81 may be constructed of any materialthat meets IEC 529 protection rating IP 65 or equivalent. In otherembodiments, terminal box 81 is integrally formed as part of the upperhousing 56.

In FIG. 6, stator assembly 60 is shown as comprising a stator core 61having twelve inward-facing teeth 41 around which are wrapped wiresextending from the three eyelet terminals 87. Before entering the statorcore 61, each of the three power conducting wires (labeled 67A, 67B, and67C) splits into two separate lead wires (multi-strand conductors),forming six wire leads designated as A1, A2, B1, B2, C1 and C2. That is,as indicated by the diagram portion of FIG. 6, wire 67A splits intoleads A1 and A2, wire 67B splits into leads B1 and B2, and wire 67Csplits into leads C1 and C2. In the embodiment shown, each lead is a21-strand, 25 American Wire Gage (25 AWG) or 0.45 mm conductor, however,other wire gages and strand counts can be used as desired to meetvarious specifications of the motor. Thus, when lead pairs A1 and A2join together, they form the power conducting wire 67A having 42strands. Power conducting wires 67B and 67C are formed in the samefashion, each having 42 strands, as well. Each of the six leads A1, A2,B1, B2, C1 and C2 wraps one of six pairs of stator teeth 41, thusforming the windings 66. The stator teeth 41 are shown as paired basedon which lead wraps around them. Thermistor leads 68 connect tothermistor probe 69, as mentioned previously, which, in the embodimentshown, is inserted into the stator core between the winding pairslabeled A1 and C2.

The paths of each of the six wire leads around stator core 61 is furtherdemonstrated in FIGS. 7 and 8. FIG. 7 represents the stator assembly 60as a two-dimensional clock-like diagram having twelve equidistant slotslabeled numerically, S1 through S12, wherein each slot represents a gapbetween two stator teeth 41, which in FIG. 7, are labeled T1 through T12in order to indicate their positions in relation to slots S1 throughS12. As shown, lead A1, at A1 Start, enters slot S1 at the top of statortooth T1, extends downward through slot S1 and wraps under stator toothT1, passes up through slot S2 between stator teeth T1 and T2, passesover the top of stator tooth T2, then passes down through slot S3between stator teeth T2 and T3, back under stator tooth T2, and finallyback up through slot S2 between stator teeth T1 and T2, to A1 Finish,thereby completing a single winding about stator teeth T1 and T2. Tobegin the second winding around teeth T1 and T2, lead A1 first passesover the top of stator tooth T1 and then repeats the winding sequenceuntil 14 total wraps are completed, ending at A1 Finish. In suchfashion, the three pairs of stator teeth identified as A1, B1 and C1 onFIG. 6 are each wound 14 times in the illustrated embodiment by wireleads A1, B1 & C1 respectively. At the conclusion of these windings, theends of wire leads A1, B1 and C1, labeled A1 Finish, B1 Finish and C1Finish in FIG. 7, and labeled A1 _(F), B1 _(F) and C1 _(F) in FIG. 8,are connected and soldered together to form a ground connection labeledas D in FIG. 8.

Just as lead A1 wraps stator teeth T1 and T2, lead B1 wraps stator teethT9 and T10, and lead C1 wraps stator teeth T5 and T6, the remainingstator teeth are wrapped by leads A2, B2 and C2. However, in this case,as shown in FIG. 7, the leads enter the slot between the two teeth theyare to wrap, extend under the first tooth, up through the gap on itsother side, over the top of the first tooth and back down through thegap between the two teeth, under the second tooth, and finally up theslot along the far side of the second tooth and back across its top tobegin a new winding or exit the winding pattern at A2 Finish, B2 Finishor C2 Finish, as applicable, when a winding is completed. Once again, inthe embodiment shown, each pair of stator teeth is wrapped 14 times. Inthis fashion, lead A2 wraps stator teeth T7 and T8, lead B2 wraps statorteeth T3 and T4, and lead C2 wraps stator teeth T11 and T12. At theconclusion of these windings, the ends of leads A2, B2, and C2, labeledA2 Finish, B2 Finish and C2 Finish in FIG. 7, and labeled A2 _(F), B2_(F) and C2 _(F) in FIG. 8, are then connected and soldered together toform a second ground connection labeled as E in FIG. 8. As each leadconsists of 21 strands, ground connections D and E each join a total of63 strands in the embodiment shown. The stator windings 66, whencompleted, preferably receive a protective coating. Though 14 wraps areused in connection with the illustrated embodiment, other numbers ofwraps are used in other embodiments as desired to alter the motorcharacteristics.

Turning to FIG. 9, a simplified perspective view of the stator assembly60 and the rotor assembly 70 are shown. For instance, the number oflaminations illustrated in both the stator and rotor are not significantand details of windings 66 and various electrical connections describedpreviously are not shown. As shown, rotor core 71 and stator core 61 areformed from a plurality of laminations that are individually stamped andthen stacked together. The stator laminations 62 are secured together byapplying adhesive between each lamination and/or welding along weldingslots 65. Rotor laminations 72 are also secured together by applyingadhesive between each lamination and/or welding. In the illustratedembodiment, individual stator laminations 62 and rotor laminations 72are punched from the same stock to reduce material waste. In otherembodiments, the stator and rotor cores 61 and 71 are each of unitaryconstruction, created by casting or other known methods in order toprovide the basic shape and structural integrity as required. However,using stacked laminations is one practical, known construction methodwhich allows the stator core 61 to take on the skewed shape that isclearly visible in the form of the slanted slots between the statorteeth 41 or in the slanted welding slots 65 along the outside surface ofstator core 61. As will be further described below, this skew givesmotor 34 certain desirable performance characteristics.

Rotor assembly 70 comprises five north polarity magnets 73 a, eachseparated by one of the five south polarity magnets 73 b. Thisalternating polarity arrangement is illustrated in FIG. 10, whichprovides a top plan view of the rotor assembly 70. In the illustratedembodiment, the ten equally-sized and shaped magnets 73 a and 73 b areformed from Neo-Boron-Iron (NdFeB) and coated to prevent oxidation. Themagnetic flux properties of rotor assembly 70 are influenced by usingrotor magnets 73 a and 73 b with convex faces as illustrated. Inaddition, the convex outer surfaces of the rotor magnets 73 a and 73 bhelp establish a proper airgap between the rotor and stator of motor 34.Electrical current passing through the windings 66 generates a rotatingelectromagnetic flux field that attracts the rotor magnets 73 a or 73 bof opposite polarity causing the rotor assembly 70 to turn as current ispassed through the windings 66 of the stator assembly 60.

The magnets 73 a and 73 b are secured to the rotor core 71 using anadhesive, but are also held in place in the embodiment shown by dovetailjoints 27 formed in rotor laminations 72. In other contemplated IPMmotor embodiments, the rotor construction may utilize magnets havingother geometric cross-sections, such as rectangular cross-sections. Withrectangular cross-sections, no special magnet surface shaping isrequired, and the magnets may be installed into rectangular openings inthe rotor core. This embedded magnet configuration improves rotordimensional stability and enables a reduction in the amount of magnetmaterial used while marginally increasing electromagnetic efficiency. Inother contemplated embodiments, the shape of the rotor core 71 and rotormagnets 73 a and 73 b may be modified such that the skew referred toabove in relation to the stator core 61 is manifested in the rotor core71. In still other contemplated embodiments, both the rotor core 71 andthe stator core 61 have a skew relative to the axis of rotor rotation.

FIG. 11 illustrates stator skew angle 63 of stator core 61. In theembodiment shown, stator skew angle 63 is nine degrees. The skew isclearly visible at the edges of the stator teeth profiles 64 sincestator laminations 62 are stacked together and each lamination isrotated slightly in relation to the previous lamination in the stackabout a common central axis. The nine-degree stator skew angle is usedin connection with this embodiment to reduce noise and vibration andimprove motor acceleration and deceleration characteristics. In thisembodiment, the nine-degree stator skew angle produces a smoother bellcurve for airgap flux-density than a non-skewed stator design as rotorassembly 70 rotates inside the skewed stator core 61. Graphicallydepicted in FIG. 12 are two exemplary airgap flux-density curves whichdemonstrate the relatively smoother operation of a motor with anine-degree stator skew versus a motor with a non-skewed stator. The twocurves shown indicate flux-density as each rotor turns through 360electrical degrees, which, in the embodiment shown, is equivalent to arotor rotation of 72 degrees about its central axis. 360 electricaldegrees, or one full electrical rotation, results from only 72 degreesof actual rotor rotation in the embodiment shown because the embodimentcontains five north/south polarity magnet pairs (360 divided by 5pairs=72 degrees). This smoother bell curve translates to a smootherrunning motor (reduced torque ripple, less cogging motion) as the motoris ramped up to operating speed.

Furthermore, the skewed stator core 61 and/or the convex shape ofmagnets 73 a and 73 b as illustrated herein contribute to a backelectromotive force (back EMF) with a sinusoidal waveform which enablessensorless speed control of motor 34. Other skew angles are desirable inother configurations or under differing load requirements or operatingenvironments. It will be understood that this invention generallycomprises the concept of skewing the stator core relative to the rotorcore and is not limited to any particular skew angle. However, high skewangles in the illustrated embodiment can cause the winding process tobecome quite difficult. Where higher angles are desired, a slotlessdesign (not shown) is used wherein the stator teeth would be inverted sothat they point outward and are encased in a sleeve. This embodiment hasan advantage where a higher skew angle is desired in that there is moreroom to insert and wrap the windings around a highly skewed stator toothprofile 64.

Now that motor 34 has been described, it will be useful to illustratehow the mechanical energy it generates is harnessed by a utility vehicleor other power equipment as contemplated herein. As shown in FIG. 5,adapter 13 is secured to motor shaft 20 by a screw or bolt 17 and awasher 16. In this case, bolt 17 and washer 16 also secure a blade 15(partially shown) by sandwiching it in the joint. Adapter 13 rotateswith motor shaft 20 and in relation to the bell nose cone portion 45 ofthe lower housing 57 in which it is nested. In addition to the use of asealed lower bearing 78, this nesting further inhibits the intrusion ofdebris into the motor housing. In other embodiments, other fasteners maybe employed. In all embodiments, the joint must withstand the axial andtorsional loads that the design may encounter during operation.Furthermore, adapter 13 may be modified in other embodiments to receivea different tool or implement.

Though adapter 13 is fixed to the motor shaft 20 as described above, thejoint may be enhanced through use of a double-D coupling interface asshown in FIG. 13. In embodiments having such an interface, motor shaft20 includes two flat surfaces 22 that mate to similar flat surfaces 26formed in the inside diameter of adapter 13. These surfaces helpdistribute torsional loads over the relatively large, flat matingsurfaces (i.e., motor shaft flat surfaces 22 and hub flat surfaces 26)to provide a longer service life. This provides a robust interface whichprevents fretting of motor shaft 20 and adapter 13. As shown in FIGS. 3and 5, a similar double-D coupling interface, including flat surfaces 18of adapter 13 and mating flat surfaces on blade 15 (or other implement)is provided in some embodiments to ensure a robust joint between adapter13 and blade 15 (or other implement). As shown in FIG. 13, a set screw14, which, when installed, seats in a recess 21 on motor shaft 20, isprovided to attach adapter 13 to shaft 20 during shipping and/or duringassembly/attachment of an implement such as blade 15 onto shaft 20. Setscrew 14 may be removed prior to attaching a blade or other implement,if desired, or left in place to serve as an assembly aid to amanufacturer attaching an implement such as blade 15.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any equivalent thereof.

What is claimed is:
 1. A vehicle, comprising: a plurality of vehiclesystems comprising a traction system and an auxiliary system; aplurality of operator interfaces for operating the vehicle eachassociated with one of the plurality of vehicle systems; a plurality ofsensors each associated with at least one of the plurality of vehiclesystems; and an electric motor control system in communication with theplurality of vehicle systems, the plurality of sensors, and theplurality of operator interfaces; wherein the auxiliary systemcomprises: an operable implement; and an electric auxiliary motorengaged with the operable implement and in communication with theelectric motor control system, the electric auxiliary motor comprising:an upper housing; a lower housing including a flange for mounting theupper housing thereon and a cone-shaped portion extending away from theflange and the upper housing; a stator assembly formed of a first corehaving a first height and fitted into the upper housing; a rotorassembly rigidly joined to a shaft to rotate therewith within the statorassembly, the rotor assembly formed of a second core having a secondheight; and a hub connected to a lower end of the shaft to rotatetherewith in relation to the cone-shaped portion, the hub beingconfigured to secure the operable implement to the electric auxiliarymotor, wherein the second height is greater than the first height. 2.The vehicle of claim 1, wherein the electric auxiliary motor furthercomprises an upper bearing fitted onto an upper end of the shaft andslip-fitted into an upper cylindrical pocket formed within the upperhousing, and a lower bearing fitted onto the lower end of the shaft andslip-fitted into a lower cylindrical pocket formed within thecone-shaped portion.
 3. The vehicle of claim 1, wherein: the first coreis formed by stacking a plurality of first laminations; the second coreis formed by stacking a plurality of second laminations; the pluralityof first laminations are skewed relatively to an axis of rotation of therotor assembly; and the plurality of second laminations are skewedrelatively to the axis of rotation of the rotor assembly.
 4. The vehicleof claim 3, wherein the rotor assembly comprises magnets which extendabove and below the stacked plurality of first laminations of the statorassembly.
 5. The vehicle of claim 2, wherein the shaft comprises upperand lower shoulders to position the upper and lower bearings,respectively.
 6. The vehicle of claim 5, wherein the shaft furthercomprises a middle shoulder to position the rotor assembly along theshaft.
 7. A vehicle, comprising: a plurality of vehicle systemscomprising a traction system and an auxiliary system; a plurality ofoperator interfaces for operating the vehicle each associated with oneof the plurality of vehicle systems; a plurality of sensors eachassociated with at least one of the plurality of vehicle systems; and anelectric motor control system in communication with the plurality ofvehicle systems, the plurality of sensors, and the plurality of operatorinterfaces; wherein the auxiliary system comprises: an implement; and anelectric auxiliary motor engaged with the implement and in communicationwith the electric motor control system, the electric auxiliary motorcomprising: an upper housing; a lower housing having a flange tosealingly receive the upper housing and an extended portion; a motorshaft having an end configured to engage an implement adapter, the endconfigured as a double-D coupling interface, the motor shaft disposed atleast partially within the upper and lower housings and supported by theextended portion of the lower housing; the implement adapter having anend configured to receive the implement, wherein the end of theimplement adapter is configured as a second double-D coupling interface;a stator assembly disposed within the upper housing; and a rotorassembly engaged to the motor shaft to rotate therewith within thestator assembly.
 8. The vehicle of claim 7, wherein: the double-Dcoupling interface comprises a pair of substantially flat surfaces forengaging with the implement adapter; and the pair of substantially flatsurfaces form opposite sides of the end of the motor shaft.
 9. Thevehicle of claim 8, wherein the implement adapter comprises a pair ofsubstantially flat receiving surfaces for engaging with the pair ofsubstantially flat surfaces of the double-D coupling interface.
 10. Thevehicle of claim 7, wherein the implement comprises a mower blade. 11.The vehicle of claim 10: further comprising a mowing deck; wherein: theflange has a plurality of fastener openings about a circumference of theflange to mount the electric auxiliary motor to the mowing deck; and themotor shaft and the implement adapter extend through the mowing deck toreceive the mower blade.
 12. The vehicle of claim 7, wherein the seconddouble-D coupling interface comprises a second pair of substantiallyflat surfaces for engaging with the implement.
 13. The vehicle of claim12, wherein the implement comprises a second pair of substantially flatreceiving surfaces for engaging with the second pair of substantiallyflat surfaces of the second double-D coupling interface.
 14. A vehicle,comprising: a plurality of vehicle systems comprising a traction systemand an auxiliary system; a plurality of operator interfaces foroperating the vehicle each associated with one of the plurality ofvehicle systems; a plurality of sensors each associated with at leastone of the plurality of vehicle systems; and an electric motor controlsystem in communication with the plurality of vehicle systems, theplurality of sensors, and the plurality of operator interfaces; whereinthe auxiliary system comprises: an operable implement; and an electricauxiliary motor engaged with the operable implement and in communicationwith the electric motor control system, the electric auxiliary motorcomprising: an upper housing; a lower housing including a flange formounting the upper housing thereon and a cone-shaped portion extendingaway from the flange and the upper housing; a shaft having an endconfigured as a double-D coupling interface; a stator assembly formed ofa first core and disposed in the upper housing; a rotor assembly engagedto the shaft to rotate therewith within the stator assembly, the rotorassembly formed of a second core; and a hub engaged to the double-Dcoupling interface to rotate therewith in relation to the cone-shapedportion, the hub being configured to secure the operable implement tothe electric auxiliary motor, wherein the hub has an end configured toreceive the operable implement, the end of the hub configured as asecond double-D coupling interface.
 15. The vehicle of claim 14,wherein: the double-D coupling interface comprises a pair ofsubstantially flat surfaces for engaging with the hub; and the pair ofsubstantially flat surfaces form opposite sides of the end of the shaft.16. The vehicle of claim 15, wherein the hub comprises a pair ofsubstantially flat receiving surfaces for engaging with the pair ofsubstantially flat surfaces of the double-D coupling interface.
 17. Thevehicle of claim 14, wherein the operable implement comprises a mowerblade.
 18. The vehicle of claim 17: further comprising a mowing deck;wherein: the flange has a plurality of fastener openings about acircumference of the flange to mount the electric auxiliary motor to themowing deck; and the shaft and the hub extend through the mowing deck toreceive the mower blade.
 19. The vehicle of claim 14, wherein the seconddouble-D coupling interface comprises a second pair of substantiallyflat surfaces for engaging with the operable implement.
 20. The vehicleof claim 19, wherein the operable implement comprises a second pair ofsubstantially flat receiving surfaces for engaging with the second pairof substantially flat surfaces of the hub.